The present invention relates to a spring-action running and jumping shoe having an upper sole and a lower sole which are connected elastically to each other.
Man's running and jumping capabilities are increased by shoes having elastic soles. For high jumps, a large spring path and large spring force are advantageous, as in trampoline jumping. Spring-action running and jumping shoes of relatively large spring path and large spring force can be used for athletic running and jumping, for jogging and for a jumping sport similar to trampoline jumping.
Many embodiments of spring-action running and jumping shoes are known. In this connection, different types of springs are used, such as coil compression springs, tension springs, leaf springs, rubber and foam-rubber cushions and pneumatic springs. With a spring path of several centimeters, the exact guidance of the lower sole which contacts the ground upon running is a problem. Expensive devices have been described in order to make certain that breaking out of the spring toward the side or toward the front and rear is prevented. When wide leaf springs or similar structural parts are used, the guidance problem is solved. Thus, German Utility Model No. 7701451 describes an embodiment which contains a leaf spring, the front half of which is developed as the outer sole, while its rear end is fastened to the rear end of the upper sole. This embodiment makes it possible upon running to improve the take-off by means of the spring force shortly before the lifting off of the foot. But, one cannot take up the momentum upon placing the heel of the foot down and use it again for the forward drive.
The opposite is true in the case of a V-shaped base fastened below the running show with its point forward, as described in German DE-OS No. 24 24 889. Upon running, the push of the heel is taken up thereby and is converted into an upward and forward thrust. The take-off is not improved thereby, since no spring action is present any longer in this position.
Both of the embodiments described furthermore have the disadvantage that only a part of the leaf spring can fully develop its spring action since it is developed in part as the outer sole. A spring calculation shows that the permissible strength values of spring steel are rapidly exceeded if it is attempted to take up with these springs the spring forces which correspond to several times the weight of the body.
From the above description it is clear that it is advantageous for a spring-action running and jumping shoe to contain two spring actions. The first spring action takes up the upward thrust when the heel is placed down and converts it into an upward and forward thrust during the course of the rolling motion of the foot. The second spring action improves the take-off with the tip of the foot. One complicated device for converting the thrust of the heel into forward thrust is described in DE-OS No. 30 12 945. Simpler embodiments having two springs are described in DE No. 30 17 769A1 and DE No. 30 34 126A1. The latter patent application also contains an embodiment having two leaf springs curved in S shape, wherein one spring is fastened to the front end and one to the rear end of the shoe. The two loose ends of the leaf springs form the outer sole. At least one of the two springs must be divided in two, for reasons of symmetry. Since the width of the shoe is not more than 10 cm, this results in relatively narrow leaf springs of only slight lateral stability. During running, such running shoes therefore tend to move out toward the side or to tilt. They have the further disadvantage that the spring action of the leaf springs is only partly utilized. Therefore, large forces cannot be taken up due to the limited strength of the material.